The present invention relates to an electronic timepiece comprising an integrated circuit with an oscillator, a frequency divider, a central circuit capable of controlling different functions of the timepiece, at least one input terminal a control logic of the display, a display unit, and control means.
In an electronic timepiece the control of the frequency of the oscillator may give rise to some problems. For example, a direct measurement of the frequency done via a sample of the signal at the quartz crystal level generally causes a small disturbance of the oscillator. On the other hand, the oscillator may be well adjusted, but the frequency divider chain may not function. It is for that reason that one generally prefers to control the running of the timepiece by sampling the signals at the end of the divider chain, before the display unit; e.g., at the output terminals which feed the motor in the case of a timepiece with a stepping motor. In a timepiece comprising a seconds hand it is quite common to find signals with a frequency of one Hertz, but not in timepiece comprising only hours and minutes hands where the period of the driving pulses may be extended, for example, to 5, 12, 20, 30 or 60 seconds. In this way, the power consumption is decreased which permits extension of the autonomy of the working of the timepiece while using batteries of small dimensions. But, when the repetition frequency of the driving signals is low, the measurement time becomes exceedingly long and the adjustment of the frequency of the oscillator, for example by way of a trimmer capacitor, becomes practically impossible.
To avoid the indicated drawbacks it is sufficient to take samples of the signals from the frequency divider chain which have an intermediate frequency such as 128 Hz. Such a signal allows a precise and rapid measurement of the frequency of the oscillator and a check of the working of the frequency divider.
However, in a watch, the number of places available for obtaining measurements is very limited, and the watch generally does not have a contact surface or output terminal adapted for connecting the signal to be measured to an external counter.
Swiss Pat. No. CH 593 513 discloses an electronic quartz crystal watch provided with a stepping motor and an electronic circuit having output terminals, normally used to deliver the driving pulses to the motor which are also used to measure the frequency of a signal delivered by the frequency divider chain. However, the solution disclosed by the Swiss patent is very specific to a timepiece provided with a stepping motor.